The present invention relates to mechanical assemblies and more particularly to those which attempt to achieve zero backlash characteristics.
Backlash is the relative motion of mechanical parts caused by looseness. Depending on the application a certain amount of backlash is tolerated so long as it does not affect the accuracy of the machine or instrument.
With advancements in scientific instruments, there is an increasing need for a zero backlash, or substantially zero backlash mechanical device. To this end a large number of devices have been developed in an effort to obtain this objective.
A simple solution is described in U.S. Pat. No. 4,589,298, entitled xe2x80x9cZero Backlash Drive Mechanismxe2x80x9d issued to Meyer et al. on May 20, 1986. This attempt at obtaining zero backlash is designed to assure that a bolt""s backlash is minimized. The technique used to spring load the bolt, thereby keeping the bolt""s threads pressed against the bore""s threads.
While this approach may work for the securing of the bolts it is totally incapable of addressing an assembly where relative motion between parts is required,
An apparatus which attempts to produce zero backlash for apparatus with relative motion is described in U.S. Pat. No. 4,221,438, entitled, xe2x80x9cBearing System for the Pivot Bar of Microtomes Particularly Ultramicrotomesxe2x80x9d issued on Sep. 9, 1980 to Sitte et al., incorporated hereto by reference.
This patent mounts two assemblies to each other by using a set of balls which are cradled by one assembly while the ball is secured to another frame. In this application, backlash is crated by the required machining of the parts. This was required because of the cradling surfaces, but, a totally matching of the cradling surfaces to the ball""s exterior surface is impossible.
It is clear from the foregoing that there is a need for an assembly which approaches zero backlash characteristics.
The invention is a hinge assembly which creates a zero backlash situation. In this context, the term xe2x80x9czeroxe2x80x9d backlash is the attempt to approach the tolerances which will accomplish a true zero backlash. Those of ordinary skill in the art readily recognize that an absolute xe2x80x9czeroxe2x80x9d is never achievable, but, is approached.
The hinge of the present invention has two major components: (1) the base member which is affixed to a stationary platform; and (2) the hinge member which moves relative to the base member.
The base member has multiple seats having two contact ridges. Each of the seats are formed by a pair of parallel (or substantially parallel) ridges. The contact ridges are spaced apart at a set distance, xe2x80x9cxxe2x80x9d. The distance x is chosen to meet the specific needs of the hinge. That is, where the hinge is small, x is less than when the hinge is larger.
The contact ridges are formed by an intersection of two planes. Ideally these planes intersect at substantially ninety degrees. The invention is not limited to only a ninety degree intersection and those of ordinary skill in the art readily recognize that this angle can be enlarged above ninety degrees, or reduced below ninety degrees.
For each seat in the base member, a ball interconnect is engaged by the contact ridges. Ideally the ball interconnect is spherical in shape and has a diameter of z. In this context, z greater than x, thereby allowing intersect ridges to contact the ball interconnect at single point.
In an alternative embodiment of the invention, the base member has manufactured into it a series of spherical xe2x80x9cbulgesxe2x80x9d or bumps which serve the same purpose of the combined base member above (with seats) and the ball interconnect.
Opposing the base member is the hinged member which as a matching set of seats, each of which is also formed by two intersecting ridges. Although ideally the intersect ridges are formed by two planes intersecting at substantially right angles, those of ordinary skill in the art readily recognize that other angels of intersection are also acceptable in this context.
The distance between the contact ridges of the hinge member is y. Relationally, y less than z, which allows the seat formed by the intersect ridges of the hinge member to xe2x80x9cridexe2x80x9d on the ball interconnect at a single point (a line meeting a sphere).
The preferred embodiment of the invention has x substantially equal to y, but, unequal values are also acceptable so long as x less than z and y less than z.
The assembly is held together by any of a number of methods obvious to those of ordinary skill in the art. The preferred technique for securing the assembly together is a spring loaded bolt which extends through the base member and is screwed into the hinge member. A spring is loaded between the base member and the head of the bolt to assure that the assembly is kept pressed against each other.
Another embodiment of the invention has the bolt extending through the hinge member and secured to the base member. Again, the bolt is spring loaded and serves the same function outlined above.
By sandwiching the ball interconnect between the contact ridges of the base member and the contact ridges of the hinge member, the elements are maintained in contact, even during movement. Zero backlash is obtained because the contact between the base unit, the ball interconnect, and the hinge member, is though a series of individual points, not a milled surface. Zero backlash is created in which firm and positive contact is maintained between the elements of the hinge.
The invention, together with various embodiments thereof, will be more filly explained by the accompanying drawings and the following description thereof.